1. Field of the Invention
This invention relates to a supercharging system for an internal combustion engine in which a part of exhaust is mixed with intake air and returned to the internal combustion engine.
2. Description of Related Art
Conventionally, EGR systems in which a part of exhaust gas is taken out of an exhaust gas system and returned to an intake system of the engine to be added to mixture gas and intake air, such as disclosed in, e.g., Japanese Unexamined Patent Publication Nos. S60-237,153, H11-62,632, H11-182,358, and 2003-286,871, have been used in engines for automobiles along with gasoline engines and diesel engines. The EGR system has a supercharger such as, e.g., a turbocharger or the like, in which a turbine of the turbocharger is driven by the exhaust gas exhausted from the internal combustion engine to render the compressor rotate to take in and compress outside air, and the compressed air is then supplied into the internal combustion engine, e.g., an engine and so on after cooled down with an intercooler. At a time of this supply, a part of the exhaust gas is taken out of the internal combustion engine to be mixed with the intake gas, and thereafter returned as an EGR gas to the internal combustion engine.
The EGR system, particularly the cooled EGR system for diesel engines of high EGR ratio such as disclosed in the Japanese Unexamined Patent Publication No. H11-108,578 has existed, in which an EGR gas cooler for cooling the EGR gas at a high temperature with cooling water, cooling air, refrigerants for automobile air conditioners, or other refrigerant liquid is disposed to reduce nitrogen oxide gas (NOx) in the exhaust gas, to prevent the mileage from becoming inferior, and to prevent functions and durability of the EGR valve from deteriorated due to excessively increased temperature.
With a supercharger such as, e.g., a turbocharger or the like, however, a structure is complicated to result in high costs while ingression of extraneous substances such as, e.g., stones, sands, etc. into a compressor or a turbine, introduction of exhaust gas at excessively high temperature, or the like occasionally causes a component such as, e.g., a bearing, a seal, a shaft, etc. to get damaged, deformed, or stuck, or causes oil to leak, so that maintenance and so on have been troublesome for taking effort and time. Furthermore, the supercharger or an intercooler needs to be formed separately from an EGR gas system, and further the EGR gas system has an EGR gas cooler, so that the EGR system becomes complicated and larger in size.
This invention is to solve the above described problems, and to obtain the supercharging system for the internal combustion engine with a simple structure and plain manufacturing art to allow reduction in product costs as well as improvement of product durability. This invention is further to enable this supercharging system to operate with use of kinetic energy of the exhaust gas, not with use of large electric power, a fuel, etc., to enhance economical efficiency. The invention is even further to enable a recirculation device such as, e.g., the EGR system or the like arranged into the internal combustion engine to reduce in size, weight, etc. and to obtain the product having superior layout property installable in limited space such as, e.g., an engine room as well as having superior durability hardly allowing occurrences of damage or deformation.